linux-kernel - Re: missing madvise functionality

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Message-ID: <4615B043.8060001@yahoo.com.au>
Date:	Fri, 06 Apr 2007 12:28:19 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ulrich Drepper <drepper@...hat.com>
CC:	Rik van Riel <riel@...hat.com>, Jakub Jelinek <jakub@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Hugh Dickins <hugh@...itas.com>
Subject: Re: missing madvise functionality

Ulrich Drepper wrote:
> In case somebody wants to play around with Rik patch or another
> madvise-based patch, I have x86-64 glibc binaries which can use it:
> 
>   http://people.redhat.com/drepper/rpms
> 
> These are based on the latest Fedora rawhide version.  They should work
> on older systems, too, but you screw up your updates.  Use them only if
> you know what you do.
> 
> By default madvise(MADV_DONTNEED) is used.  With the environment variable

Cool. According to my thinking, madvise(MADV_DONTNEED) even in today's
kernels using down_write(mmap_sem) for MADV_DONTNEED is better than
mmap/mprotect, which have more fundamental locking requirements, more
overhead and no benefits (except debugging, I suppose).

MADV_DONTNEED is twice as fast in single threaded performance, and an
order of magnitude faster for multiple threads, when MADV_DONTNEED only
takes mmap_sem for read.

Do you plan to include this change in general glibc releases? Maybe it
will make google malloc obsolete? ;) (I don't suppose you'd be able to
get any tests done, Andrew?)

-- 
SUSE Labs, Novell Inc.
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